1. Field of the Invention
The present invention relates to a lead used in an integrated circuit device, a method of assembling an integrated circuit device using the lead, an integrated circuit device thereby obtained, a lead for providing a conductive path from an electrode on a substrate and a method of providing a conductive path.
2. Description of the Background Art
FIG. 9 is a front elevational view of a conventional hybrid integrated circuit device. The hybrid integrated circuit device comprises a first circuit substrate 11 such as a thick film substrate, an electronic part 14 disposed on the first circuit substrate 11, a lead 1 extending perpendicularly from an edge of the first circuit substrate 11, a second circuit substrate 10 such as a printed board and a through-hole electrode 9 formed on the second circuit substrate 10. The lead 1 comprises an upper portion 3 having a clip 2 and a lower portion 4 including a tapered stopper 6 indicated by the shaded portion and a thin tip 7. The lead 1 is soldered to the through-hole electrode 9 by flow soldering while the tip 7 is inserted into the through-hole electrode 9. As shown in FIG. 10 looking from the left side of FIG. 9, the clip 2 holds the edge of the first circuit substrate 11 between upper and lower arms thereof. FIG. 11 is a plan view of FIG. 9. The upper arm of the clip 2 abuts a connecting pad 15 formed on the first circuit substrate 11.
When the lead 1 is soldered to the second circuit substrate 10 by flow soldering, solder 8 rises along the tip 7 of the lead 1 through a slight opening between the through-hole electrode 9 and the tip 7 inserted therein. However, when a back side of the second circuit substrate 10 is dipped into flux, the flux cannot reach the stopper 6. Therefore, in the next step of dipping the back side of the second circuit substrate 10 into fused solder, the solder hardly rises to the stopper 6.
When a vibration test (with vibrating power 4.4 G, in three directions respectively for 2 hours) is executed and the stopper 6 is not fixed by solder 8, the lead 1 experiences bending deformation over and over again at a fulcrum at the through-hole electrode 9 formed on the printed board 10 and the stopper 6 of the lead 1, and eventually fractures thereat. As the length of the lead 1 becomes longer so as to provide sufficient space between the first circuit substrate 11 and the second circuit substrate 10 for mounting some parts not only on a front surface of the second circuit substrate 10 but also on a back surface of the first circuit substrate 11, the bending deformation grows more serious and causes the lead 1 to fracture easily.
Accordingly, a conventional process of fabricating a hybrid integrated circuit device needs another steps of raising the solder to the stopper 6 of the lead 1 and/or coating a portion of the lead 1 subject to bending deformation with proper resin after the lead 1 is soldered by flow soldering so as to reinforce the lead 1.